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Semester 4 - Clinical Neuroscience > 10. The Reticular Formation and Consciousness > Flashcards

10. The Reticular Formation and Consciousness Flashcards

1
Q

Define consciousness.

A

Define consciousness.

awareness of external environment and internal states

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2
Q

Define arousal.

A

Associated with goal-seeking behaviour and avoidance of noxious stimuli

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3
Q

What 2 neural components are required for consciousness?

A

Cerebral cortex and reticular formation

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4
Q

What are the cortex and reticular formation connected by and what does it form?

A

Connected by reciprocal excitatory projections forming a positive feedback loop

  • binary outcome
  • awake/not awake etc
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5
Q

what is the role of cerebral cortex in consciousness?

A

the site where conscious thoughts arise

􏰀 Receives many inputs, including from the reticular formation

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6
Q

what is the role of reticular formation in consciousness?

A

the circuitry that keeps the cortex ‘awake’

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7
Q

What are 2 important inputs to the reticular formation?

A

Cortex and sensory systems

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8
Q

What is the reticular formation?

A

A population of specialised interneurones in the brainstem

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9
Q

What are the 3 major output pathways of the reticular formation and what neurotransmitter is involved?

A

Cholinergic (excitatory fibres) to:

  • basal forebrain nuclei
  • hypothalamus
  • thalamus
  • (also down to the spinal cord, maintaining muscle tone)
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10
Q

What type of fibres project from the basal forebrain nuclei ?

A

excitatory cholinergic fibres to cortex

- (think sedative side effects of anticholinergics)

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11
Q

What type of fibres project from the hypothalamus?

A

excitatory histaminergic fibres to the cortex

- (think sedative side-effects of sedating antihistamines)

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12
Q

What type of fibres project from the thalamus?

A

excitatory glutamatergic fibres to the cortex

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13
Q

What is the part of the reticular system involved in arousal called?

A

Reticular activating system

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14
Q

What is used for clinical assessment of consciousness?

A

Glasgow Coma Scale (GCS)

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15
Q

What are the components of GCS?

A
  1. eye opening
  2. motor response
  3. verbal response
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16
Q

How is Eye Opening scored on GCS and what do they suggest?

A
  • Spontaneous eye opening (4) suggests normal cortical and brainstem function
  • Response to speech (3) suggests slightly diminished cortical function but still functioning brainstem
  • Response to pain (2) suggests impaired cortical function but brainstem preserved so that reflex opening can occur
  • No response (1) suggests severe damage to brainstem +/- cortex
17
Q

How is motor response scored on GCS and what do they suggest?

A
  • Obeys commands (6) suggests normal function with working connections from auditory system to brainstem/cord
  • Localises to stimuli (5) suggests diminished higher cortical function but still connections working from sensory to motor cortex
  • Withdraws to pain (4) suggests that there is still a ‘physiological’ reflex response to stimuli
  • Flexor response to pain (3) suggests a lesion above the level of the red nuclei. This response is still ‘semiphysiological’
  • Extensor response to pain (2) suggests a lesion below the red nuclei. This response is not physiological at all
  • No response to pain (1) suggests severe damage to brainstem +/- cortex
18
Q

How is verbal response scored on GCS and what do they suggest?

A
  • Oriented in time/place (5) suggests normal cortical function
  • Confused conversation (4) suggests diminished higher cortical function but language centres are still functioning adequately
  • Inappropriate words (3) suggests language centres have been damaged
  • Incomprehensible sounds (2) suggests cortical damage with brainstem mediated groans
  • No response (1) suggests severe damage to brainstem +/- cortex
19
Q

What is the electroencephalogram?

A

Measures the combined activity of thousands of neurones in a particular region of cortex

  • high temporal resolution
  • low spatial resolution
20
Q

What are electroencephalograms good for detecting?

A

Good for detecting neuronal synchrony, and evidence of normal cerebral function

21
Q

How many stages of sleep are there?

A

4 major stages + REM sleep

22
Q

How does awake with eyes open present on an EEG?

A

Beta waves - irregular, 50Hz

23
Q

How does awake with eyes closed present on an EEG?

A

Alpha waves - regular, 10Hz

24
Q

How does stage 1 sleep present on an EEG?

A

Background of alpha + interspersed theta waves (theta at around 5Hz, regular)

25
Q

How does stage 2/3 sleep present on an EEG?

A

Background of theta + interspersed sleep spindles and k-complexes:

  • Sleep spindles are high frequency bursts arising from the thalamus
  • K-complexes represent the emergence of the ‘intrinsic rate’ of the cortex
26
Q

How does stage 4 sleep present on an EEG?

A

Delta waves - regular, 1Hz

- Related to k-complexes seen in stages 2/3

27
Q

How does REM sleep present on an EEG?

A
  • EEG similar to beta waves

- Dreaming occurs in this stage, so similar to the EEG in a conscious patient

28
Q

What is the neural mechanism of (non-REM) sleep and what helps facilitate it?

A
  • Complex
  • Deactivation of the reticular activating system (and hence cortex) + inhibition of the thalamus
  • This deactivation is facilitated by removal of sensory inputs (fewer positive influences on positive feedback loop)
29
Q

What is REM sleep initiated by?

A

Initiated by neurones in the pons (i.e. initiation appears to be an active process)

30
Q

What is the EEG of REM similar to, why is it difficult to wake a person in REM sleep?

A
  • similar to awake, eyes open

- difficult to rouse due to strong thalamic inhibition

31
Q

What is the muscle tone during REM sleep and why?

A

Decreased muscle tone due to descending inhibition of LMNs by glycinergic fibres arising from the reticular formation and running down the reticulospinal tracts

32
Q

What cranial nerve functions may be preserved during REM sleep?

A
  • Eye movements

- teeth grinding (nocturnal bruxism)

33
Q

What are some autonomic effects during REM sleep?

A
  • Penile erection,

- loss of thermoregulation (homeless hypothermia)

34
Q

What does long term deprivation of REM sleep lead to?

A

Death

35
Q

What are some functions of sleep? (4)

A

Generally unknown

  • Energy conservation / repair?
  • Memory consolidation?
  • Clearance of extracellular debris? (bulk movement of interstitial fluid into CSF)
  • ‘Resetting’ of the CNS?
36
Q

Give 3 examples of sleep disorders.

A
  • insomnia
  • narcolepsy (may be caused by mutations in orexin gene)
  • sleep apnoea (daytime sleepiness)
37
Q

what is insomnia commonly caused by?

A

underlying psychiatric disorder as opposed to ‘primary’ insomnia

38
Q

what is sleep apnoea commonly caused by?

A

excess neck fat leading to compression of airways during sleep and frequent waking

39
Q

excess neck fat leading to compression of airways during sleep and frequent waking

A
  • locked in syndrome
  • persistent vegetative state (PVS)
  • coma
  • brain death

Semester 4 - Clinical Neuroscience (19 decks)

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